Planning a sojourn in the northeastern United States? You could soon be taking part in a novel security programme that can supposedly ‘sense’ whether you are planning to commit a crime.

Future Attribute Screening Technology (FAST), a US Department of Homeland Security (DHS) programme designed to spot people who are intending to commit a terrorist act, has in the past few months completed its first round of field tests at an undisclosed location in the northeast, Nature has learned.

Like a lie detector, FAST measures a variety of physiological indicators, ranging from heart rate to the steadiness of a person’s gaze, to judge a subject’s state of mind. But there are major differences from the polygraph. FAST relies on non-contact sensors, so it can measure indicators as someone walks through a corridor at an airport, and it does not depend on active questioning of the subject.

The tactic has drawn comparisons with the science-fiction concept of ‘pre-crime’, popularized by the film Minority Report, in which security services can detect someone’s intention to commit a crime. Unlike the system in the film, FAST does not rely on a trio of human mutants who can see the future. But the programme has attracted copious criticism from researchers who question the science behind it (see Airport security: Intent to deceive?).

From fiction to fact

So far, FAST has only been tested in the lab, so successful field tests could lend some much-needed data to support the technology. “It is encouraging to see an effort to develop a real empirical base for new technologies before any policy commitments are made,” says Tom Ormerod, a psychologist in the Investigative Expertise Unit at Lancaster University, UK. Such testing, he adds, could lay the groundwork for a more rigorous randomized, controlled, double-blind study.

According to a privacy-impact statement previously released by the DHS, tests of FAST involve instructing some people passing through the system to carry out a “disruptive act”. Ormerod questions whether such role-playing is representative of real terrorists, and also worries that both passengers and screeners will react differently when they know they’re being tested. “Fill the place with machines that go ping, and both screeners and passengers start doing things differently.”

In lab tests, the DHS has claimed accuracy rates of around 70%, but it remains unclear whether the system will perform better or worse in field trials. “The results are still being analysed, so we cannot yet comment on performance,” says John Verrico, a spokesman for the DHS. “Since this is an ongoing scientific study, tests will continue throughout coming months.”

Some scientists question whether there really are unique signatures for ‘malintent’ — the agency’s term for the intention to cause harm — that can be differentiated from the normal anxieties of travel. “Even having an iris scan or fingerprint read at immigration is enough to raise the heart rate of most legitimate travellers,” says Ormerod.

Steven Aftergood, a senior research analyst at the Federation of American Scientists, a think-tank based in Washington DC that promotes the use of science in policy-making, is pessimistic about the FAST tests. He thinks that they will produce a large proportion of false positives, frequently tagging innocent people as potential terrorists and making the system unworkable in a busy airport. “I believe that the premise of this approach — that there is an identifiable physiological signature uniquely associated with malicious intent — is mistaken. To my knowledge, it has not been demonstrated,” he says. “Without it, the whole thing seems like a charade.”

As for where precisely FAST is being tested, that for now remains a closely guarded secret. The DHS says that although the first round was completed at the end of March, more testing is in the works, and the agency is concerned that letting people know where the tests are taking place could affect the outcome. “I can tell you that it is not an airport, but it is a large venue that is a suitable substitute for an operational setting,” says Verrico.